Mobile terminals such as a mobile phone, a Personal Digital Assistant (PDA) and the like are driven by rechargeable batteries due to their nature, and the battery of the mobile terminal is charged via supplied electronical energy by using a separate charging device. Typically, the charging device and the battery have separate contact terminals at an exterior thereof, respectively, and are electrically connected with each other by contacting the contact terminals.
However, in such a contact-type charging scheme, the contact terminals protrude outwardly, and thus are easily contaminated by foreign substances. As a result, battery charging is not correctly performed. Also, charging may not be correctly performed when the contact terminals are exposed to moisture.
Recently, a wireless charging or a non-contact charging technology has been developed and used for many electronic devices to solve the above-mentioned problems.
The wireless charging technology uses wireless power transmission and reception, and corresponds to, for example, a system in which a battery is automatically charged if the battery is simply put on a charging pad without connecting the mobile phone to a separate charging connector. Generally, a wireless vibrating toothbrush, a wireless electric shaver, and the like are known to the general public. The wireless charging technology can improve a waterproof function because it can be used to wirelessly charge the electronic devices. The wireless charging technology can improve the portability of the electronic devices because it does not require a wired charger. Therefore, it is expected that technologies related to the wireless charging technology will be significantly developed in the coming age of electric cars.
The wireless charging technology largely includes an electromagnetic induction scheme using a coil, a resonance scheme using a resonance, and an RF/microwave radiation scheme converting electrical energy to a microwave and then transmitting the microwave.
It is considered up to now that the electromagnetic induction scheme is mainstream, but it is expected that the day will come when all electronic products are wirelessly charged, anytime and anywhere, without a wire in the near future on the strength of recent successful experiments for wirelessly transmitting power to a destination spaced away by dozens of meters through the use of microwaves at home and abroad.
A power transmission method through the electromagnetic induction corresponds to a scheme of transmitting electric power between a first coil and a second coil. When a magnet is moved in a coil, an induction current is generated. By using the induction current, a magnetic field is generated at a transmitting end, and an electric current is induced according to a change in the magnetic field so as to generate energy at a receiving end. The phenomenon is referred to as magnetic induction, and the power transmission method using magnetic induction has a high energy transmission efficiency.
A resonance scheme is a wireless charging scheme using resonance. It is known that the resonant electrical energy does not affect surrounding machines or human bodies differently from other electromagnetic waves because the resonant electrical energy is directly transferred only to a device having a resonance frequency and unused parts are reabsorbed into an electromagnetic field instead of spreading into the air.